The present invention relates to a piston of internal combustion engine.
Japanese Patent Application Publication No. 2011-132809 (hereinafter, referred to as patent document 1) discloses a previously-proposed piston of internal combustion engine.
In this technique, the piston is integrally formed of aluminum alloy. This piston includes a pair of thrust-side and counter-thrust-side skirt portions, a pair of apron portions, and a crown portion on which a combustion chamber is defined. The pair of thrust-side and counter-thrust-side skirt portions are integrally formed with the crown portion. Each of the pair of thrust-side and counter-thrust-side skirt portions slides on a surface of cylinder wall and is formed in an arc shape in cross section. The pair of apron portions are respectively connected with circumferential both ends of the pair of skirt portions, and include pin boss portions. A concave portion is formed inside an upper end portion of the apron portion, and moreover, a necking portion (waisted portion) is provided at a lower portion of the concave portion. By this necking portion, a stiffness of at least a crown-portion-side part of the skirt portion is reduced for the purpose of suppressing an intensive contact between the cylinder wall and the crown-portion-side part of the skirt portion so as to reduce a friction.